The literature describing vitamin D content of fat tissue is extremely limited. We conducted a pilot study that measured the concentrations of vitamin D(3) in the fat tissue and serum of obese adults. These measurements were performed using a new liquid chromatography mass spectrometry (LC/MS) method. The objectives of this study were: to measure and report the vitamin D(3) concentration in serum and subcutaneous fat samples from obese individuals and to examine the association of vitamin D(3) in fat with vitamin D(3) in serum. This cross-sectional study was conducted in 17 obese men and women who were scheduled to undergo gastric bypass surgery. The mean vitamin D(3) concentration in subjects' subcutaneous fat tissue samples was 102.8 +/- 42.0 nmol/kg. The mean vitamin D(3) concentration in serum was 7.78 +/- 3.99 nmol/l. Vitamin D(3) concentrations of fat tissue and serum were positively correlated (r = 0.68, P = 0.003). Consistent with previous findings in obese subjects, subjects in this study had suboptimal vitamin D status as demonstrated by a mean 25-hydroxyvitamin D concentration of 43.3 +/- 15.4 nmol/l. In conclusion, fat tissue vitamin D(3) can be measured by LC/MS and is detectable in obese subjects with suboptimal vitamin D status. Compatible with the long-standing concept that fat tissue is a storage site for vitamin D, fat tissue and serum vitamin D(3) concentrations were positively correlated.

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The intestinal absorption of folate occurs at the monoglutamyl level, and an important measure of food folate bioavailability is how much folate from the food reaches the intestinal sites in forms that can readily be absorbed. In the absence of protecting agents, e.g., vitamin C and reduced thiols, many labile folates may be lost during cooking and during residence in the acid-peptic milieu of the stomach. On the other hand, the presence of polyglutamyl folate necessitates the action of intestinal hydrolases, which could be affected by food constituents. In this study, we developed an in vitro assay for the determination of an index of food folate availability. The index of folate availability in this study was defined as that proportion of folate that has been identified as monoglutamyl derivatives after tests for stability and susceptibility to an enzymatic hydrolysis. The index of folate availability varied widely among foods. The highest index was for egg yolk (72.2%), followed by cow's livers (55.7%), orange juice (21. 3%), cabbage (6.0%), lima beans (4.5%) and lettuce (2.9%). Yeast folate had the lowest index (0.3%). The availability indices generated by this study correlate with the indices of the bioavailability of the corresponding food folate observed in earlier studies, R2 = 0.529 (P = 0.068). Additional information is required on the bioavailability of other food products to test the usefulness of this in vitro approach for assessing food folate availability.